Hi, I bought a whole bunch of American-pressed 45 RPM singles off the internet from the 1980's. They seem to play fine, but I am noticing something strange:

They all seem to have weird bubbling on the 45 LABEL itself. Does anyone know the source of this damage? Could a jukebox have caused it or water damage?

The bubbling or puckering can be felt as raised patches when I run my finger around the label. The print is legible, and there is no discoloration. It's almost like the glue or adhesive holding the label down, bubbled up in places, like a pizza. Any idea what caused it? Thank you.